Studies of the effects of IL-12 on CTL differentiation were continued. Synergistic interactions with IL-7 were explored. Studies of the effects of IL-2, IL-4, IL-7, IL-12, and IL-15 on NK and T cell activation were begun in conjunction with ongoing studies of effects of other cytokines.Studies of the timing dependent ability of IL-4 to block and to promote CTL differentiation of CD8 cells in a high efficiency cloning system were continued. The OKT3 hybridoma cell line was subcloned to generate clones with improved stability in surface antibody production and optimized for use as stimulators or targets for CTL. We have engaged in collaborative efforts with WHO and other laboratories to develop and characterize an international standard for IL-4. The dependence and independence of T cell leukemias for IL-2 and the relationship of tyrosine kinase signal transduction pathways of T cell leukemias were explored.